Cell Migration from Baby to Mother

Fetal cells migrate into the mother during pregnancy. Fetomaternal transfer probably occurs in all pregnancies and in humans the fetal cells can persist for decades. Microchimeric fetal cells are found in various maternal tissues and organs including blood, bone marrow, skin and liver. In mice, fetal cells have also been found in the brain. The fetal cells also appear to target sites of injury. Fetomaternal microchimerism may have important implications for the immune status of women, influencing autoimmunity and tolerance to transplants. Further understanding of the ability of fetal cells to cross both the placental and blood-brain barriers, to migrate into diverse tissues, and to differentiate into multiple cell types may also advance strategies for intravenous transplantation of stem cells for cytotherapeutic repair. Here we discuss hypotheses for how fetal cells cross the placental and blood-brain barriers and the persistence and distribution of fetal cells in the mother.Key Words: fetomaternal microchimerism, stem cells, progenitor cells, placental barrier, blood-brain barrier, adhesion, migrationMicrochimerism is the presence of a small population of genetically distinct and separately derived cells within an individual. This commonly occurs following transfusion or transplantation.^1–3 Microchimerism can also occur between mother and fetus. Small numbers of cells traffic across the placenta during pregnancy. This exchange occurs both from the fetus to the mother (fetomaternal)^4–7 and from the mother to the fetus.^8–10 Similar exchange may also occur between monochorionic twins in utero.^11–13 There is increasing evidence that fetomaternal microchimerism persists lifelong in many child-bearing women.^7,14 The significance of fetomaternal microchimerism remains unclear. It could be that fetomaternal microchimerism is an epiphenomenon of pregnancy. Alternatively, it could be a mechanism by which the fetus ensures maternal fitness in order to enhance its own chances of survival. In either case, the occurrence of pregnancy-acquired microchimerism in women may have implications for graft survival and autoimmunity. More detailed understanding of the biology of microchimeric fetal cells may also advance progress towards cytotherapeutic repair via intravenous transplantation of stem or progenitor cells.Trophoblasts were the first zygote-derived cell type found to cross into the mother. In 1893, Schmorl reported the appearance of trophoblasts in the maternal pulmonary vasculature.¹⁵ Later, trophoblasts were also observed in the maternal circulation.^16–20 Subsequently various other fetal cell types derived from fetal blood were also found in the maternal circulation.^21,22 These fetal cell types included lymphocytes,²³ erythroblasts or nucleated red blood cells,^24,25 haematopoietic progenitors^7,26,27 and putative mesenchymal progenitors.^14,28 While it has been suggested that small numbers of fetal cells traffic across the placenta in every human pregnancy,^29–31 trophoblast release does not appear to occur in all pregnancies.³² Likewise, in mice, fetal cells have also been reported in maternal blood.^33,34 In the mouse, fetomaternal transfer also appears to occur during all pregnancies.³⁵     

Molecular functions of the PP2A regulatory subunit Tap46 in plants

Tap42/α4 is a regulatory subunit of the protein phosphatase 2A (PP2A) family of phosphatases and plays a role in the target of rapamycin (TOR) pathway that regulates cell growth, ribosome biogenesis, translation and cell cycle progression in both yeast and mammals. We determined the cellular functions of Tap46, the plant homolog of Tap42/α4, in both Arabidopsis thaliana and Nicotiana benthamiana. Tap46 associated with the catalytic subunits of PP2A and the PP2A-like phosphatases PP4 and PP6 in vivo. Tap46 was phosphorylated by TOR in vitro, indicating that Tap46 is a direct substrate of TOR kinase. Tap46 deficiency caused cellular phenotypes that are similar to TOR-depletion phenotypes, including repression of global translation and activation of both autophagy and nitrogen recycling. Furthermore, Tap46 depletion regulated total PP2A activity in a time-dependent manner similar to TOR deficiency. These results suggest that Tap46 acts as a positive effector of the TOR signaling pathway in controlling diverse metabolic processes in plants. However, Tap46 silencing caused acute cell death, while TOR silencing only hastened senescence. Furthermore, mitotic cells with reduced Tap46 levels exhibited chromatin bridges at anaphase, while TOR depletion did not cause a similar defect. These findings suggest that Tap46 may have TOR-independent functions as well as functions related to TOR signaling in plants.Key words: acute cell death, autophagy, chromatin bridge, nitrogen mobilization, protein phosphatases, target of rapamycin (TOR)Yeast type 2A phosphatase-associated protein 42 kDa (Tap42) is a regulatory subunit that directly associates with catalytic subunits of the protein phosphatase 2A (PP2A) family of protein phosphatases to make a heterodimer and regulates the activity and substrate specificity of the intact enzyme complex.¹ Functions of Tap42 as a component of the target of rapamycin (TOR) signaling pathway have been well characterized in yeast.^1–3 Tap42-regulated phosphatase activities play a major role in signal transduction mediated by TOR. Accumulating evidence suggest that TOR regulates phosphorylation of target proteins by restraining PP2A activity through Tap42 phosphorylation.^1–3 Rapamycin inhibits TOR activity and also influences Tap42-mediated phosphatase regulation in yeast.^3–5α4, the mammalian homolog of Tap42, also associates with the catalytic subunits of PP2A, PP4 and PP6 to make a heterodimer.⁶ Rapamycin inhibits mammalian TOR (mTOR) activity, but it is not clear whether rapamycin prevents the formation of the α4/PP2Ac complex or whether α4 stimulates or represses PP2Ac activity.^7–9 Interestingly, loss of Tap42 function in Drosophila does not affect TOR-regulated activities, including cell growth, metabolism and S6 kinase activity, but results in mitotic arrest caused by spindle anomalies and subsequent activation of c-Jun N-terminal kinase signaling and apoptosis.¹⁰ Similarly, α4 deletion in mice leads to the rapid onset of apoptosis in both proliferating and differentiated cells, while rapamycin itself does not severely affect adult cells.¹¹ Furthermore, while TOR depletion causes developmental arrest and organ degeneration at the L3 stage in Caenorhabditis elegans, loss of α4 does not reproduce TOR deficiency phenotypes, but mainly leads to a fertility defect.¹² Taken together, these results suggest that the yeast Tap42/TOR paradigm is not completely conserved in higher eukaryotes and that Tap42/α4 functions may not be exclusively dependent on the Tor signaling pathway.In this study, we investigated the in vivo functions and phosphatase regulation of Tap46, the plant Tap42/α4 homolog, in relation to TOR in Nicotiana benthamiana, Arabidopsis and tobacco BY2 cells. Tap46 was shown to interact with the catalytic subunits of PP2A, PP4 and PP6 in vivo. Recombinant Tap46 protein was phosphorylated by immunoprecipitated TOR kinase and its deletion forms in vitro. Dexamethasone-induced RNAi of Tap46 caused dramatic repression of global translation and activation of both autophagy and nitrogen mobilization in the early stages of gene silencing. These phenotypes mimic those of TOR inactivation or TOR deficiency in Arabidopsis, yeast and mammals, indicating that Tap46 is a critical mediator of the Tor pathway in the regulation of these metabolic processes in plants. However, these early phenotypes of Tap46-deficient plants were soon followed by an acute and rapid programmed cell-death (PCD), while TOR silencing only led to growth retardation and premature senescence in Arabidopsis and N. benthamiana, confirming results from a previous study.¹³ The PCD caused by Tap46 deficiency is consistent with the apoptosis induced by loss of Tap42/α4 function in both Drosophila and mice.^10,11 Thus Tap42/α4/Tap46 appears to have a strong anti-apoptotic activity in higher eukaryotes. The underlying mechanisms of PCD activation caused by Tap46 depletion remain to be revealed, but it is possible that the inappropriate modulation of phosphatase activity and aberrant protein phosphorylation led to stress signaling and PCD activation.Another interesting phenotype of Tap46 deficiency is the formation of chromatin bridges in anaphase during mitosis, suggesting a role for Tap46 in plant cell mitotic progression. However, there have been no reports of anaphase bridge formation in tor mutants of any organisms. In Drosophila, loss of Tap42 function causes spindle disorganization and pre-anaphase arrest prior to the onset of apoptosis.¹⁰ In addition, Drosophila mutants with a defective regulatory subunit of PP2A exhibit an increased number of lagging chromosomes and chromatin bridges in anaphase.^14,15 Tap46 likely regulates the functions of PP2A family phosphatases during mitosis by direct association with their catalytic subunits, thereby modulating both the activity and specificity of the enzyme. Accumulating evidence reveals dynamic functions of PP2A during mitosis in both yeast and mammals: PP2A regulates kinetochore function, sister chromatid cohesion, spindle bipolarity and progression to anaphase.^15–17 Counteracting the activity of protein kinases, PP4 has also been implicated in both centrosome maturation and function during mitosis.¹⁸ Based on immunolabeling results, Tap46 was visualized as distinct spots around chromatin and mitotic spindles during mitosis in tobacco BY2 cells (Lee HS and Pai HS, unpublished results). Further studies will address the interacting partners and dynamic relocation of Tap46 during the cell cycle.Our results in this study demonstrated that Tap46 plays an important regulatory role in plant growth and metabolism; a major part of its function appears related to TOR signaling. However, we consistently observed certain phenotypic differences between Tap46-silenced and TOR-silenced Arabidopsis and N. benthamiana plants: an acute and rapid PCD occurred upon Tap46 silencing but not upon TOR silencing, despite a similar degree of gene silencing. Furthermore, we did not observe anaphase bridge formation in mitotic root-tip cells of ethanol-induced TOR RNAi Arabidopsis plants, while chromatin bridges were repeatedly observed in Tap46-silenced tobacco BY2 and Arabidopsis root-tip cells. Although an ancient Tap42/TOR paradigm observed in yeast appears to be conserved in plants, new TOR-independent functions of Tap46 might have evolved, the abrogation of which can cause massive PCD activation and anaphase bridge formation. Tap46 is a major regulator of cellular PP2A activity in plant cells by interacting with multiple phosphatase partners. Unraveling the molecular networks of Tap46 activity and interactions is essential for understanding its TOR-dependent and -independent functions in plants.     

RALFs: Peptide regulators of plant growth

Peptide signaling regulates a variety of developmental processes and environmental responses in plants.^1–6 For example, the peptide systemin induces the systemic defense response in tomato⁷ and defensins are small cysteine-rich proteins that are involved in the innate immune system of plants.^8,9 The CLAVATA3 peptide regulates meristem size¹⁰ and the SCR peptide is the pollen self-incompatibility recognition factor in the Brassicaceae.^11,12 LURE peptides produced by synergid cells attract pollen tubes to the embryo sac.⁹ RALFs are a recently discovered family of plant peptides that play a role in plant cell growth.Key words: peptide, growth factor, alkalinization     

Complete Genome Sequence of Croceibacter atlanticus HTCC2559T

Here we announce the complete genome sequence of Croceibacter atlanticus HTCC2559^T, which was isolated by high-throughput dilution-to-extinction culturing from the Bermuda Atlantic Time Series station in the Western Sargasso Sea. Strain HTCC2559^T contained genes for carotenoid biosynthesis, flavonoid biosynthesis, and several macromolecule-degrading enzymes. The genome confirmed physiological observations of cultivated Croceibacter atlanticus strain HTCC2559^T, which identified it as an obligate chemoheterotroph.The phylum Bacteroidetes comprises 6 to ∼30% of total bacterial communities in the ocean by fluorescence in situ hybridization (8-10). Most marine Bacteroidetes are in the family Flavobacteriaceae, most of which are aerobic respiratory heterotrophs that form a well-defined clade by 16S rRNA phylogenetic analyses (4). The members of this family are well known for degrading macromolecules, including chitin, DNA, cellulose, starch, and pectin (17), suggesting their environmental roles as detritus decomposers in the ocean (6). Marine Polaribacter and Dokdonia species in the Flavobacteriaceae have also shown to have photoheterotrophic metabolism mediated by proteorhodopsins (11, 12).Several strains of the family Flavobacteriaceae were isolated from the Sargasso Sea and Oregon coast, using high-throughput culturing approaches (7). Croceibacter atlanticus HTCC2559^T was cultivated from seawater collected at a depth of 250 m from the Sargasso Sea and was identified as a new genus in the family Flavobacteriaceae based on its 16S rRNA gene sequence similarities (6). Strain HTCC2559^T met the minimal standards for genera of the family Flavobacteriaceae (3) on the basis of phenotypic characteristics (6).Here we report the complete genome sequence of Croceibacter atlanticus HTCC2559^T. The genome sequencing was initiated by the J. Craig Venter Institute as a part of the Moore Foundation Microbial Genome Sequencing Project and completed in the current announcement. Gaps among contigs were closed by Genotech Co., Ltd. (Daejeon, Korea), using direct sequencing of combinatorial PCR products (16). The HTCC2559^T genome was analyzed with a genome annotation system based on GenDB (14) at Oregon State University and with the NCBI Prokaryotic Genomes Automatic Annotation Pipeline (15, 16).The HTCC2559^T genome is 2,952,962 bp long, with 33.9 mol% G+C content, and there was no evidence of plasmids. The number of protein-coding genes was 2,715; there were two copies of the 16S-23S-5S rRNA operon and 36 tRNA genes. The HTCC2559^T genome contained genes for a complete tricarboxylic acid cycle, glycolysis, and a pentose phosphate pathway. The genome also contained sets of genes for metabolic enzymes involved in carotenoid biosynthesis and also a serine/glycine hydroxymethyltransferase, which is often associated with the assimilatory serine cycle (13). The potential for HTCC2559^T to use bacterial type III polyketide synthase (PKS) needs to be confirmed because this organism had a naringenin-chalcone synthase (CHS) or chalcone synthase (EC 2.3.1.74), a key enzyme in flavonoid biosynthesis. CHS initiates the addition of three molecules of malonyl coenzyme A (malonyl-CoA) to a starter CoA ester (e.g., 4-coumaroyl-CoA) (1) and takes part in a few bacterial type III polyketide synthase systems (1, 2, 5, 18).The complete genome sequence confirmed that strain HTCC2559^T is an obligate chemoheterotroph because no genes for phototrophy were found. As expected from physiological characteristics (6), the HTCC2559^T genome contained a set of genes coding for enzymes required to degrade high-molecular-weight compounds, including peptidases, metallo-/serine proteases, pectinase, alginate lyases, and α-amylase.     

Why have chloroplasts developed a unique motility system?

Organelle movement in plants is dependent on actin filaments with most of the organelles being transported along the actin cables by class XI myosins. Although chloroplast movement is also actin filament-dependent, a potential role of myosin motors in this process is poorly understood. Interestingly, chloroplasts can move in any direction and change the direction within short time periods, suggesting that chloroplasts use the newly formed actin filaments rather than preexisting actin cables. Furthermore, the data on myosin gene knockouts and knockdowns in Arabidopsis and tobacco do not support myosins'' XI role in chloroplast movement. Our recent studies revealed that chloroplast movement and positioning are mediated by the short actin filaments localized at chloroplast periphery (cp-actin filaments) rather than cytoplasmic actin cables. The accumulation of cp-actin filaments depends on kinesin-like proteins, KAC1 and KAC2, as well as on a chloroplast outer membrane protein CHUP1. We propose that plants evolved a myosin XI-independent mechanism of the actin-based chloroplast movement that is distinct from the mechanism used by other organelles.Key words: actin, Arabidopsis, blue light, kinesin, myosin, organelle movement, phototropinOrganelle movement and positioning are pivotal aspects of the intracellular dynamics in most eukaryotes. Although plants are sessile organisms, their organelles are quickly repositioned in response to fluctuating environmental conditions and certain endogenous signals. By and large, plant organelle movements and positioning are dependent on actin filaments, although microtubules play certain accessory roles in organelle dynamics.^1,2 Actin inhibitors effectively retard the movements of mitochondria,^3–6 peroxisomes,^5,7–11 Golgi stacks,^12,13 endoplasmic reticulum (ER),^14,15 and nuclei.^16–18 These organelles are co-aligned and associated with actin filaments.^{5,7,8,10–12,15,18} Recent progress in this field started to reveal the molecular motility system responsible for the organelle transport in plants.¹⁹Chloroplast movement is among the most fascinating models of organelle movement in plants because it is precisely controlled by ambient light conditions.^20,21 Weak light induces chloroplast accumulation response so that chloroplasts can capture photosynthetic light efficiently (Fig. 1A). Strong light induces chloroplast avoidance response to escape from photodamage (Fig. 1B).²² The blue light-induced chloroplast movement is mediated by the blue light receptor phototropin (phot). In some cryptogam plants, the red light-induced chloroplast movement is regulated by a chimeric phytochrome/phototropin photoreceptor neochrome.^23–25 In a model plant Arabidopsis, phot1 and phot2 function redundantly to regulate the accumulation response,²⁶ whereas phot2 alone is essential for the avoidance response.^27,28 Several additional factors regulating chloroplast movement were identified by analyses of Arabidopsis mutants deficient in chloroplast photorelocation.^29–32 In particular, identification of CHUP1 (chloroplast unusual positioning 1) revealed the connection between chloroplasts and actin filaments at the molecular level.²⁹ CHUP1 is a chloroplast outer membrane protein capable of interacting with F-actin, G-actin and profilin in vitro.^29,33,34 The chup1 mutant plants are defective in both the chloroplast movement and chloroplast anchorage to the plasma membrane,^22,29,33 suggesting that CHUP1 plays an important role in linking chloroplasts to the plasma membrane through the actin filaments. However, how chloroplasts move using the actin filaments and whether chloroplast movement utilizes the actin-based motility system similar to other organelle movements remained to be determined.Open in a separate windowFigure 1Schematic distribution patterns of chloroplasts in a palisade cell under different light conditions, weak (A) and strong (B) lights. Shown as a side view of mid-part of the cell and a top view with three different levels (i.e., top, middle and bottom of the cell). The cell was irradiated from the leaf surface shown as arrows. Weak light induces chloroplast accumulation response (A) and strong light induces the avoidance response (B).Here, we review the recent findings pointing to existence of a novel actin-based mechanisms for chloroplast movement and discuss the differences between the mechanism responsible for movement of chloroplasts and other organelles.     

Hypoxia: A novel function for VIN3

VERNALIZATION INSENSITIVE 3 (VIN3) encodes a PHD domain chromatin remodelling protein that is induced in response to cold and is required for the establishment of the vernalization response in Arabidopsis thaliana.¹ Vernalization is the acquisition of the competence to flower after exposure to prolonged low temperatures, which in Arabidopsis is associated with the epigenetic repression of the floral repressor FLOWERING LOCUS C (FLC).^2,3 During vernalization VIN3 binds to the chromatin of the FLC locus,¹ and interacts with conserved components of Polycomb-group Repressive Complex 2 (PRC2).^4,5 This complex catalyses the tri-methylation of histone H3 lysine 27 (H3K27me3),^4,6,7 a repressive chromatin mark that increases at the FLC locus as a result of vernalization.^4,7–10 In our recent paper¹¹ we found that VIN3 is also induced by hypoxic conditions, and as is the case with low temperatures, induction occurs in a quantitative manner. Our experiments indicated that VIN3 is required for the survival of Arabidopsis seedlings exposed to low oxygen conditions. We suggested that the function of VIN3 during low oxygen conditions is likely to involve the mediation of chromatin modifications at certain loci that help the survival of Arabidopsis in response to prolonged hypoxia. Here we discuss the implications of our observations and hypotheses in terms of epigenetic mechanisms controlling gene regulation in response to hypoxia.Key words: arabidopsis, VIN3, FLC, hypoxia, vernalization, chromatin remodelling, survival     

Novel protein-protein interaction family proteins involved in chloroplast movement response

To optimize photosynthetic activity, chloroplasts change their intracellular location in response to ambient light conditions; chloroplasts move toward low intensity light to maximize light capture and away from high intensity light to avoid photodamage. Although several proteins have been reported to be involved in chloroplast photorelocation movement response, any physical interaction among them was not found so far. We recently found a physical interaction between two plant-specific coiled-coil proteins, WEB1 (Weak Chloroplast Movement under Blue Light 1) and PMI2 (Plastid Movement Impaired 2), that were indentified to regulate chloroplast movement velocity. Since the both coiled-coil regions of WEB1 and PMI2 were classified into an uncharacterized protein family having DUF827 (DUF: Domain of Unknown Function) domain, it was the first report that DUF827 proteins could mediate protein-protein interaction. In this mini-review article, we discuss regarding molecular function of WEB1 and PMI2, and also define a novel protein family composed of WEB1, PMI2 and WEB1/PMI2-like proteins for protein-protein interaction in land plants.Key words: Arabidopsis, blue light, chloroplast velocity, coiled-coil region, organelle movement, phototropin, protein-protein interactionIntracellular locations of chloroplasts change in response to different light conditions to capture sunlight efficiently for energy production through photosynthesis. Chloroplasts move toward weak light to maximize light capture (the accumulation response),^1,2 and away from strong light to reduce photodamage (the avoidance response).³ In higher plants such as Arabidopsis thaliana, the responses are induced by blue light-dependent manner.^1,2 Recently, chloroplast actin (cp-actin) filaments were found to be involved in chloroplast photorelocation movement and positioning.^4,5 The cp-actin filaments are localized at the interface between the chloroplast and the plasma membrane to anchor the chloroplast to the plasma membrane, and are relocalized to the leading edge of chloroplasts before and during the movement.^4,5 The difference of cp-actin filament amounts between the front and the rear halves of chloroplasts determines the chloroplast movement velocity; as the difference increases, chloroplast velocity also increases.^4,5Several proteins have been reported to be involved in chloroplast movement. The blue light receptors, phototropin 1 (phot1) and phot2, mediate the accumulation response,⁶ and phot2 solely mediates the avoidance response.^7,8 Chloroplast Unusual Positioning 1 (CHUP1), Kinesin-like Protein for Actin-Based Chloroplast Movement 1 (KAC1) and KAC2 are involved in the cp-actin filament formation.^4,9–11 Other proteins with unknown molecular function involved in the chloroplast movement responses have also been reported. They are J-domain Protein Required for Chloroplast Accumulation Response 1 (JAC1),^12,13 Plastid Movement Impaired 1 (PMI1),¹⁴ a long coiled-coil protein Plastid Movement Impaired 2 (PMI2), a PMI2-homologous protein PMI15,¹⁵ and THRUMIN1.¹⁶Recently, we characterized two plant-specific coiled-coil proteins, Weak Chloroplast Movement under Blue Light 1 (WEB1) and PMI2, which regulate the velocity of chloroplast photorelocation movement.¹⁷ In this mini-review article, we discuss about molecular function of WEB1 and PMI2 in chloroplast photorelocation movement, and also define the WEB1/PMI2-related (WPR) protein family as a new protein family for protein-protein interaction.     

Protein interactors of acyl-CoA-binding protein ACBP2 mediate cadmium tolerance in Arabidopsis

In our recent paper in the Plant Journal, we reported that Arabidopsis thaliana lysophospholipase 2 (lysoPL2) binds acyl-CoA-binding protein 2 (ACBP2) to mediate cadmium [Cd(II)] tolerance in transgenic Arabidopsis. ACBP2 contains ankyrin repeats that have been previously shown to mediate protein-protein interactions with an ethylene-responsive element binding protein (AtEBP) and a farnesylated protein 6 (AtFP6). Transgenic Arabidopsis ACBP2-overexpressors, lysoPL2-overexpressors and AtFP6-overexpressors all display enhanced Cd(II) tolerance, in comparison to wild type, suggesting that ACBP2 and its protein partners work together to mediate Cd(II) tolerance. Given that recombinant ACBP2 and AtFP6 can independently bind Cd(II) in vitro, they may be able to participate in Cd(II) translocation. The binding of recombinant ACBP2 to [¹⁴C]linoleoyl-CoA and [¹⁴C]linolenoyl-CoA implies its role in phospholipid repair. In conclusion, ACBP2 can mediate tolerance to Cd(II)-induced oxidative stress by interacting with two protein partners, AtFP6 and lysoPL2. Observations that ACBP2 also binds lysophosphatidylcholine (lysoPC) in vitro and that recombinant lysoPL2 degrades lysoPC, further confirm an interactive role for ACBP2 and lysoPL2 in overcoming Cd(II)-induced stress.Key words: acyl-CoA-binding protein, cadmium, hydrogen peroxide, lysophospholipase, oxidative stressAcyl-CoA-binding proteins (ACBP1 to ACBP6) are encoded by a multigene family in Arabidopsis thaliana.¹ These ACBP proteins are well studied in Arabidopsis in comparison to other organisms,^1–4 and are located in various subcellular compartments.¹ Plasma membranelocalized ACBP1 and ACBP2 contain ankyrin repeats that have been shown to function in protein-protein interactions.^5,6 ACBP1 and ACBP2 which share 76.9% amino acid identity also confer tolerance in transgenic Arabidopsis to lead [Pb(II)] and Cd(II), respectively.^1,5,7 Since recombinant ACBP1 and ACBP2 bind linolenoyl-CoA and linoleoyl-CoA in vitro, they may possibly be involved in phospholipid repair in response to heavy metal stress at the plasma membrane.^5,7 In contrast, ACBP3 is an extracellularly-localized protein⁸ while ACBP4, ACBP5 and ACBP6 are localized to cytosol.^9,10 ACBP1 and ACBP6 have recently been shown to be involved in freezing stress.^9,11 ACBP4 and ACBP5 bind oleoyl-CoA ester and their mRNA expressions are lightregulated.^12,13 Besides acyl-CoA esters, some ACBPs also bind phospholipids.^9,11,13 To investigate the biological function of ACBP2, we have proceeded to establish its interactors at the ankyrin repeats, including AtFP6,⁵ AtEBP⁶ and now lysoPL2 in the Plant Journal paper. While the significance in the interaction of ACBP2 with AtEBP awaits further investigations, some parallels can be drawn between those of ACBP2 with AtFP6 and with lysoPL2.